polyester Imported 【LIGHT & COMPACT】- Designed for cyclists, runners, hikers and group outings, this hydration pack is compact and aerodynamic. It offers featherweight stability with minimal wind drag, supporting top performance—ideal for intense activities like marathon training. 【INSULATED WATER BACKPACK】- With efficient insulation, it keeps water at an ideal temperature for up to 4 hours. Whether you need a quick sip mid-activity or steady all-day hydration, it’s your perfect outdoor companion. 【2L HYDRATION BLADDER】- Comes with a built-in 2L water bladder crafted from food-grade PEVA, free of BPA for safe hydration.Its large capacity meets hydration needs during long workouts. The high-flow bite valve allows you to drink on the go, keeping you hydrated for optimal sports performance. 【SAFETY FIRST】- For early morning/evening runs, the running vest has front/back reflective strips to boost low-light visibility. It also includes an integrated emergency whistle—blow quickly in emergencies to signal for help. These two features offer double protection and peace of mind. 【VERSATILE FOR SPORTS】- This hydration backpack is ideal for various outdoor activities, including trail running, hiking, cycling, marathons, and jogging. With its portable and form-fitting design, it works great for both men and women in all kinds of outdoor sports. KUYOU Hydration Running Vest: Crafted for Runners, Cyclists and Hikers Designed for outdoor enthusiasts, the KUYOU Hydration Backpack combines lightweight durability with burden-free carrying. The 2L large-capacity water bladder meets all-day hydration needs for sports, while the bite-valve suction design allows one-handed water replenishment anytime. Reflective strips and a built-in survival whistle offer dual protection, keeping you safe from dawn to dusk.Whether tackling mountain trails or trekking through forests, KUYOU is your reliable sports companion.